No one disputes this fact - indeed, neighbors say they saw him working in his yard that day. What is in dispute, however, is what role, if any, Mr. Nichols played in events leading up to the bombing. How that question is answered in Nichols's trial, beginning today with jury selection in Denver, will resonate well beyond the wood-paneled walls of this Western courtroom.

The conviction and sentencing to death of Timothy McVeigh, Nichols's co-defendant in the trial, was widely seen as a message to terrorists - that they would be dealt with in the severest manner possible. But in Nichols's trial, the government will be hard-pressed to construct such an emphatic case.

"Conspiracy cases are hard to prove in general," says Frank Jamison, a law professor at the University of Denver and a former Colorado judge. "Anytime you have a conspiracy, and the guy wasn't there at the time, it becomes a real tough case for the prosecution."

Like Mr. McVeigh, Nichols is charged with 11 counts of murder and conspiracy in the Oklahoma City blast that claimed 168 lives, and he could face the death penalty if convicted. And while the Nichols trial may seem like a replay of McVeigh's - identical charges, many of the same witnesses, the same judge, and most of the same prosecutors - there are significant differences.

What's different

Perhaps most important will be the trial's focus on how involved Nichols was in the bomb plot. One way the defense is expected to try to get an acquittal is to show that he was a reluctant participant in planning the bombing, and then opted out well in advance of the crime.

Testimony from Michael Fortier, a key witness in the McVeigh trial, suggests Nichols "wanted out" of the plan and even refused to help McVeigh construct the bomb. Still, unless Nichols can convince jurors that he didn't expect McVeigh to follow through with the bombing, he would still be liable for failing to alert authorities, says Mimi Wesson, a University of Colorado law professor and former US attorney.

"The challenge for Nichols's attorneys will be to prove that his efforts to pull back from the plot went far enough," she says.

Another key difference will be the caliber of the defense team, says Denver criminal defense attorney David Lane.

Nichols's court-appointed lawyer, Michael Tigar, is one of the nation's premier defense attorneys. Mr. Tigar, a University of Texas law professor, won his first case before the Supreme Court at 28 and led the successful defense in a number of prominent cases.

McVeigh's homespun lead attorney, Stephen Jones - a partner in an Enid, Okla., firm - was comparatively inexperienced, says Mr. Lane. And going up against Tigar, prosecutors may well find it tougher to get a conviction.

Tigar will likely focus on individual differences between Nichols and McVeigh. While McVeigh was generally depicted as a drifter and social outcast who became increasingly dissatisfied with the government, the defense will portray Nichols as a dedicated father of three and a successful businessman.

But the central issue of the defense will, of course, be that Nichols was hundreds of miles away when the bomb went off.

Then two days later, after hearing his name on television, Nichols drove to the local police station and submitted himself to 9-1/2 hours of questioning without a lawyer present. No guilty man would do that, Tigar says.

'So what?'

But the response from prosecutors is roughly equivalent to, "So what?" They have heard Tigar's refrain so many times they've coined it the "Terry-Nichols-wasn't-there" defense.

Government evidence suggests Nichols used the name Mike Havens to buy forty 50-pound bags of ammonium nitrate fertilizer - one of the chief ingredients used to build the Oklahoma City bomb. Prosecutors also allege Nichols stole blasting caps and 300 sticks of dynamite from a Kansas quarry. And witnesses say a dark-blue GMC pickup truck - identical to one Nichols owns - was parked next to a yellow Ryder truck at Geary Lake near Junction City, Kan., the day before the blast. Investigators believe Nichols helped McVeigh mix the bomb, and they also say Nichols then helped McVeigh plant a getaway car in Oklahoma City.

The government will also seek to underscore similarities between Nichols and McVeigh: Noting how Nichols struggled to find a niche in society, and how, after joining the Army and leaving it, he became ever-more critical of the establishment. They will also tell how Nichols began attending militia meetings and even renounced his citizenship in 1992.

But whether such sentiments translate to a reasonable motive will be up to the jurors to decide.